1. Field of the Invention
The present invention relates to an improvement in the intermediate transfer body of a transfer type recording apparatus such as transfer type electrophotographic copying machine.
2. Description of the Prior Art
FIG. 1 shows the intermediate transfer body 1 of a transfer type recording apparatus. Typical conventional intermediate transfer body used hitherto includes a substrate made of a metal such as a stainless steel or a resin, e.g. polyimide, polyester or the like and an intermediate transfer layer made of a material such as fluoro-carbon rubber, e.g. TEFLON manufactured by Du Pont, silicone rubber or the like formed on the substrate.
Besides the intermediate transfer body 1 having the form of an endless belt, the copying machine has a drive roller 2 for driving the intermediate transfer body 1, a heat source 3 incorporated in the drive roller 2, a tension roller 4 for imparting a tension to the intermediate transfer body 1, a pressure roller 5 for pressing the surface of the intermediate transfer body 1 against the surface of a photosensitive drum 6 as a toner image retaining member, a charging device 7, a projection device for projecting light 8, a developing device 9, a charge eliminating device 10, a cleaning device 11, a pressure conveyor roller 12 for pressing a recording paper 13 onto the surface of the intermediate transfer body 1 and feed the same in cooperation with the heated drive roller 2, and a conveyor roller 14 for conveying the recording paper 13.
In operation, the photosensitive drum 6 is rotated in the direction of the arrow so that the surface thereof is electrostatically charged uniformly. An electrostatic latent image formed on the charged surface as the light 8 is projected onto the charged surface. The latent image is then developed by the developing device 9. When the developed toner image 15 reaches the position of the pressure roller 5, it is transferred to the surface of the intermediate transfer body 1 and the transferred toner image 15' is further transferred to the recording paper 13 as the same is brought to the position of the pressure conveyor roller 12 as a result of movement of the intermediate transfer body 1 in the direction of the arrow.
The transferred image is then fixed on the recording paper 13 by the heat from the drive roller 2 to become a fixed toner image 15". In the above case, it is possible to heat the pressure conveyor roller 12 and the drive roller 2 as heating roller.
In this recording apparatus, the following disadvantages (1) to (4) are brought about by the use of the intermediate transfer body 1 having a metallic substrate.
(1) Since the metallic substrate exhibits a high rigidity, the intermediate transfer body 1 exhibits only a small adherence to the photosensitive drum 6 and the recording paper 13. As a result, the efficiency of the transfer of the image, particularly the image transfer from the photosensitive drum 6, is lowered seriously. To obviate this problem, it has been necessary to increase the contact pressure of the pressure roller 5.
(2) Due to the high thermal conductivity of the metallic substrate, the heat is transmitted to other portion than the pressure conveyor roller 12 so that the thermal efficiency of the heat source 3 is lowered and the temperature in the apparatus is raised undesirably.
(3) The fluoro-carbon rubber, silicone rubber or the like material constituting the surface of the intermediate transfer body exhibits only a small strength of bonding to the substrate.
(4) It is difficult to obtain the intermediate transfer body in the form of an endless belt.
It is possible to obtain higher bonding strength by using a high molecule resin such as polyimide, polyester or the like as the material of the substrate of intermediate transfer body 1 than that exhibited when the substrate is made of a metal. However, the thermosetting resin such as polyimide can provide only a small productivity because, in such a case, the intermediate transfer body is formed by a batch type method employing a mould. In addition, the intermediate transfer body made of a thermosetting resin exhibits a small adherence to the photosensitive drum 6 and to the recording paper 13. On the other hand, the intermediate transfer body having a substrate made of a thermoplastic resin such as polyester can be produced at a higher productivity than that having substrate made of a metal or even that having a substrate made of a thermosetting resin. In addition, it is easy to produce an intermediate transfer body in the form of an endless belt and, in addition, a superior adherence to the photosensitive drum 6 and the recording paper 13 is attained. Unfortunately, however, the intermediate transfer body having a substrate made of a thermoplastic resin exhibits inferior physical properties at high temperature in the fixing of the toner image.